1. Technical Field of the Invention
The present invention relates to a structure of a magnetic bearing that supports a rotor without making contact, particularly a stator core for a homo-polar type of magnetic bearing, and a method of manufacturing it.
2. Prior Art
A turbo compressor can be made larger in capacity and smaller in size than a reciprocating or screw compressor, and can be easily made to an oil-free type. Therefore, turbo compressors are used often as general-purpose compressors in applications such as a compressed air source for factories, a source of air for separation, and other various processes.
Conventionally, gas bearings, sliding bearings and magnetic bearings have been used to support a high-speed rotating shaft of a high-speed motor that is connected directly to and drives a turbo compressor. In particular, a homo-polar magnetic bearing can be used to support a rotor (rotating shaft) in a contact free manner that rotates to form the high speed shaft of a high speed motor by passing magnetic flux through the shaft to produce an electromagnetic sucking force which causes the shaft to float, this being one type of radial magnetic bearing for use with shafts that rotate at a high speed (for instance, 100,000 minxe2x88x921 or more).
FIGS. 1A and 1B show typical schematic viewes of a conventional homo-polar magnetic bearing. In these figures, a homo-polar magnetic bearing 1 is composed of a rotor 3 that is arranged at the axial center of a casing 2 and parallel to it in the axial direction and can rotate at a high speed, U-shaped stator cores 4 installed inside the casing 2 with gaps between the outer surface of the rotor 3, and coils 5 that are placed around the toothed ends of the stator cores 4.
In addition, a plurality of stator cores (4 cores in FIGS. 1A and 1B) are disposed equally spaced in the circumferential direction with gaps between the outer surface of the rotor 3. Although not illustrated, stator cores 4 are arranged in the axial direction of the rotor 3 in at least 2 locations with a predetermined distance between them. Consequently, the rotor can rotate stably at a high speed. A stator core 4 is made of laminated steel sheets each of which is manufactured with an insulating adhesive material applied to its surface to bond to an adjacent thin steel sheet, and these are bonded one after another to obtain a predetermined length. As shown in FIGS. 1A and 1B, the direction A in which the laminated steel sheets 4 (lamination) are bonded is arranged to be perpendicular to the axial direction Z of the rotor 3.
As described above, in the homo-polar magnetic bearing 1, since the toothed ends of the stator cores 4 that surround the rotor 3 are close to each other in the axial direction and as the coils 5 produce the N and S poles of an electro magnet, the homo-polar magnetic bearing 1 can float the shaft in a contact free manner and support the rotor 3 by the sucking force of the toothed ends located opposite each other. Therefore, the direction of this homo-polar magnetic field is parallel to the centerline of the rotor and on the outer surface of the rotor 3 as shown by the dashed arrow lines in FIG. 1B.
FIG. 1C is a schematic view that shows a conventional process for assembling laminated steel sheets to form a conventional stator core. Normally, the stator core 4 of the homo-polar magnetic bearing 1 is manufactured by making thin rectangular steel sheets 4a coated with an insulating material, by a method such as punching, and assembling these punched steel sheets 4a one after another, to produce a laminated stator core 4.
However, when the inner surfaces of the aforementioned stator cores 4 (laminated steel sheets) are cut by a rotary cutting process, a large cutting load is applied to the edges of the laminated steel sheets 4a in a lateral direction, so the tips of the laminated steel sheets 4a are bent, and the insulating material is crushed in the direction of rotation by the above-mentioned bending load, which is a practical problem. Consequently, the steel sheets contact each other resulting in an increase in the eddy currents in the stator unit, so another problem occurs due to the reduced levitation force applied to the rotor 3, poor rotating characteristics, etc. Still another problem is that the laminated material is peeled away by the edge of the cutting tool. Even if the above-mentioned process of cutting in a lathe is replaced by using a vertical boring machine etc. to cut the inner surfaces of laminated steel sheets, because there are gaps between adjacent steel sheets, there is the additional problems that smooth cutting and true roundness cannot be easily ensured.
On the other hand, the inventors of the present invention have proposed the homo-polar magnetic bearing apparatus configured as shown in FIGS. 2 and 3, with the aim of improving the characteristics of conventional homo-polar magnetic bearings (unpublished Japanese patent application No. 88402/2000). According to this magnetic bearing apparatus, adjacent N poles or S poles are connected together in the circumferential direction, or are located close to each other with a small gap between them. The homo-polar magnetic bearing with this configuration has the advantage that it is capable of greatly reducing the production of eddy currents and the heat and eddy current losses generated in the rotor.
However, if the stator cores 4 of the homo-polar magnetic bearing shown in FIGS. 2 and 3 are produced using laminated steel sheets with small eddy current losses, as shown in FIG. 1, the laminated steel sheets become so thin in the peripheral web 4b that they fail, crush or peel when processed, which is a practical disadvantage.
More explicitly, in the homo-polar magnetic bearing with the structure shown in FIGS. 2 and 3, the stator cores 4 are connected together circumferentially or located close to each other, so the distribution of magnetic flux in the rotor is more uniform and losses can be reduced. Conversely, however, if stator cores 4 in which the tips are connected together are formed with a conventional laminated structure, the laminated steel sheets are so small in the portions where adjacent magnetic poles are connected together that the laminated structure may collapse when the cores are machined, therefore, it is very difficult to machine the cores without detaching, crushing or peeling the laminations.
Another problem in a conventional apparatus is that amorphous materials cannot be used because they are difficult to laminate, despite the advantages of having a high electrical resistance and permeability, so the choice of electromagnetic sheet steel is restricted.
Next, the structure of a conventional homo-polar radial magnetic bearing is described in more detail than before by referring to FIGS. 4 and 5. FIG. 4a is a front view of a conventional homo-polar radial magnetic bearing, and FIG. 4b is the corresponding side sectional elevation. FIG. 5 is an isometric view of the stator core of a conventional homo-polar radial magnetic bearing.
The homo-polar radial magnetic bearing 1 is provided with a casing 2, a plurality of electromagnetic components 13 and a rotating shaft 3. The rotating shaft 3 is made of a material which is magnetic at least on the surface thereof, with an outer diameter of D1 and a length determined by the rotor. The rotor 3 is disposed coaxially with the centerline of the casing 2, parallel thereto in the longitudinal direction, and is supported so that it can rotate freely. The plurality of electromagnetic components 13 support the rotor 3 so that it can rotate freely, and are arranged around the rotor 3. For instance, four electromagnetic components are connected together to form a set, and sets of electromagnetic components 13 support the rotor 3 at 2 locations. At each supporting location, 4 electromagnetic components are equally spaced around the rotor.
The electromagnetic components 13 are provided with stator cores 80 and coils 5. The stator core 80 is provided with two yokes 6 and 8 and a stem portion 7 as shown in FIG. 5. A yoke 6 or 8 is a column-shaped portion one end of which is opposite the outer surface of the rotor 3 with a gap between them that induces a magnetic pole on the surface 9. The two yokes 6, 8 are arranged axially with a predetermined spacing between each other. The stem portion 7 is a magnetic structure between the other ends of the two yokes 6, 8 connecting the yokes together. The stator core 80 is a thick U-shaped unit comprised of the two yokes 6, 8 and the stem portion 7 without gaps, and is installed in a recess on the inner periphery of the casing 2.
The coil 5 is a bundle of wire. The wire is wound in several layers around the yokes 6, 8 with an air gap between the coil and yoke. The coil 5 is a block with the same shape as the section of the yoke 6 or 8 with an air gap between the coil and yoke.
The structure of the stator core 80 is described in further detail referring to FIG. 5. The stator core 80 is made of laminated steel sheets, consisting of a plurality of magnetic steel sheets 81 and an insulating material. The magnetic steel sheet 81 is a thin steel sheet with a thickness T, shaped in the aforementioned U shape. The insulating material is a non-conducting material and is applied between the plurality of magnetic steel sheets 81. When the stator core 80 is assembled as an electromagnetic component, it is laminated in the circumferential direction of the rotor. The magnetic steel sheet 81 of the illustrated stator core 80 is rectangular in shape with a width W1 and a height H1, provided with a slot W2 wide and H2 in height, on the side forming the magnetic pole surface 9. The stator core 80 is made of a plurality of laminated magnetic steel sheets 81 with a predetermined length of L1.
In another type of electromagnetic component, the width of a stator core 80 near the magnetic pole surface 9 is extended circumferentially in the direction of the outer surface of the rotor, and comes in close contact with the magnetic pole surfaces of the adjacent electromagnetic components of the stator core.
According to still another type of electromagnetic component, the width of a stator core 80 near the magnetic pole surface 9 is extended circumferentially in the direction of the outer surface of the rotor, and is integrated with the magnetic pole surface of an adjacent electromagnetic component of the stator core 80.
When the aforementioned stator core for a magnetic bearing is manufactured, thin sheet steel with a thickness T is punched using dies, to produce U-shaped magnetic steel sheets.
Next, the magnetic pole surface 9 of the stator core for a magnetic bearing must be machined into a circular arc using a lathe etc.; at this time, the rotation causes a cutting load that acts laterally on the edges of the laminated steel sheets, so the tips of the electromagnetic steel sheets are bent; due to this bending, the insulation material is crushed in the direction of rotation, often resulting in adjacent electromagnetic steel sheets coming in contact with each other. The problem encountered when this happens is that large eddy currents are produced in the electromagnetic steel sheets.
Another problem that the laminated steel sheets become separated during cutting, may occur.
There is also another problem that if a vertical boring machine is used instead of a lathe, differences are produced at the edges between adjacent laminated steel sheets, and a true, smooth circle cannot be ensured.
With the type of stator core for a magnetic bearing in which the magnetic pole surface of the stator core is extended over the outer surface of the rotor, since the laminated steel sheets in the extended portions become very thin, they may cause problems by becoming detached, crushed or peeled during machining.
The present invention aims at solving the aforementioned problems. That is, the first object of the present invention is to provide a stator core for a magnetic bearing, such that even if there are portions extended circumferentially around the core, the core can be made with laminated steel sheets, can avoid the laminated steel sheets becoming detached, crushed or peeled, can be efficiently cut and processed, can also be made of an amorphous material which cannot otherwise be easily laminated, thus enabling the manufacturing and processing costs to be reduced, and can greatly reduce the eddy currents generated in the stator core, and the manufacturing method thereof.
The second object of the present invention is to offer a stator core for a magnetic bearing, that has a structure which allows a high utilization of the component material, or the core can be processed with high precision, or one in which the generation of eddy currents is kept to a minimum.
To achieve the above-mentioned first object, the present invention provides such a stator core for a magnetic bearing that is a stator core for a homo-polar magnetic bearing in which the toothed ends of the stator cores are close to each other in the axial direction and form N poles and S poles, wherein the stator cores (10) have portions (11) protruding from adjacent N poles and S poles that are extended circumferentially so as to be in contact with or in close proximity to each other and are made of laminated steel sheets that are interspaced with an insulating material and have a U-shape which is open on the center side when viewed from the side of the shaft.
Using this configuration, the production of eddy currents can be drastically reduced, thereby the rotor losses, due to the heat generated by the eddy currents can be greatly reduced. Because the stator core (10) is composed of laminated steel sheets with a U shape such that the center side is open when viewed from the side of the axis of the shaft, even the protruding portions (11) that are in contact with or are located close to each other can be integrated into one body together with the coils. Therefore, the laminated steel in the protruding tips (protruded portions) can be an integral part of the same steel sheet as that in the location of the coils, so a laminated structure can withstand processing work without becoming collapsed, and also avoiding becoming detached, crushed or peeled, thereby the sheet can be efficiently cut and processed.
Moreover, because the cores can be processed after being formed and cut, even an amorphous material etc. that cannot be easily laminated can be used.
According to a preferred embodiment of the present invention, the aforementioned U-shaped laminated steel cores (12) are manufactured from a continuous steel sheet (12a) coated with an insulation material that is wound into a rectangular shape and then cut into equal parts.
Using this configuration, such stator cores (10) have protruding portions (11) composed of adjacent N and S poles extending circumferentially so as to be in contact with or in close proximity to each other and are composed of U-shaped laminated steel sheets with an insulating material between the laminations and the U shape is such that the center side is open when viewed from the side of the shaft, the cores can be processed quickly and efficiently by processing the outer shape and cutting the inside of the cut cores (12).
In addition, the cut cores (12), are wound into a rectangular shape with a center opening of predetermined dimensions and can be formed quickly and easily. Moreover, by dividing this wound rectangular shape, into two equal parts with a cutting machine, U-shaped laminated steel sheets each of which is isolated with an insulating material can be easily fabricated. Furthermore, high-cost punching dies need not be used, but simple and compact wrapping dies can be used to manufacture the cut cores, so the manufacturing costs can be reduced, laminating work can be omitted, and therefore, productivity can be improved. In addition, the scrap material that might otherwise be produced from the center parts of steel sheets during punching work when using punching dies can be avoided, therefore, the yield of steel sheets can be improved drastically.
In addition, the present invention presents a method of manufacturing cores for a magnetic bearing, including an outside machining step (A) wherein the outside surfaces of the cut cores (12) fabricated by wrapping a continuous steel sheet coated with an insulating material into a rectangular shape and then cut into equal parts are machined to leave protrusions (11), a coil assembling step (B) for assembling coils onto cut cores after the outside has been machined, a core assembling step (C) in which a plurality of cut cores are assembled at the required locations, and an inner cutting step (D) for cutting the inside of a plurality of cut cores after assembly at the required locations.
Using the aforementioned method, cutting the inside of a plurality of cut cores can be completed in one operation, and the cores can be machined with an excellent concentricity. In addition, the inner surfaces of the ends of the teeth can be cut in the direction of the sheet laminations and in the plane of the laminations during rotation, without imposing a biasing or bending load, therefore, the cut surfaces of the steel sheets remain smooth and regular without the insulating material becoming crushed, broken or peeled, so that a satisfactory excellent roundness can be preserved.
In addition, the present invention offers a method of manufacturing cores for a magnetic bearing, that includes an inside cutting step (E) wherein a plurality of cut cores (12) fabricated by wrapping a continuous steel sheet coated with an insulating material into a rectangular shape and, forming and cutting it into equal parts are assembled in the required positions and the inside thereof is cut, an outside machining step (F) in which the outside of the plurality of cut cores are machined leaving protrusions (11), and a coil assembling step (G) wherein the plurality of cut cores of which the outside has been machined are fitted with coils.
According to this method of the present invention, cutting the inner surface is required twice, however, the number of machining steps can be reduced. In addition, when the inner periphery of the toothed ends is cut during rotation, the cutting work can be carried out in the direction of the lamination and in the horizontal plane of the steel sheets on the inner periphery of the toothed ends, without producing a bias load or deflection, therefore, the cut edges of the steel sheets can be kept smooth without any irregularity at the edge of each cut, and the peripheries of the cores can be kept smooth and truly circular without any collapsing, tearing or peeling of the insulating material.
To achieve the aforementioned second object of the present invention, the invention provides stator cores for a magnetic bearing, composed of a first yoke (6) that is used for a homo-polar magnetic bearing for supporting a rotor (3) provided with a supporting surface made of a magnetic material, and one end of which forms the magnetic pole surface opposite the above-mentioned supporting surface with a predetermined width to pass magnetic flux, that is, a first pole body, a second yoke (8) one end of which forms a magnetic pole surface opposite the aforementioned supporting surface with a predetermined width to pass the magnetic flux, that is, a second pole body, and a stem unit (7) that is arranged between and in close contact with the other ends of the above-mentioned first yoke and the aforementioned second yoke and passes the magnetic flux between them, wherein the aforementioned first yoke (6) and the above-mentioned second yoke (8) are regularly arranged opposite each other in the lateral direction of the aforementioned pole body, and at least the stem unit (7) is fabricated from a magnetic material powder, solidified in a resin.
Using this configuration, since the first yoke (6), stem unit (7) and second yoke (8) are integrated into a U-shape and the stem unit (7) is made of the magnetic material powder solidified in resin, when the magnet is energized, the flux passes through the first yoke (6), rotor (3), second yoke (8) and stem unit (7), in a closed path; since the magnetic pole surfaces at the ends of the first yoke (6) and the second yoke (8) support the rotor (3) at the supporting surfaces, and as the magnetic material powder solidified in resin produces only a small amount of eddy current loss, eddy currents are not generated in the stem unit (7), so a magnetic bearing with few losses can be realized.
In the stator cores for a magnetic bearing according to the present invention, the aforementioned first pole body (6) is a laminated body in which magnetic steel sheets are laminated in the direction orthogonal to a line normal to the above-mentioned magnetic pole surface, interleaved with a non-conducting substance, and the above-mentioned second pole body (8) is a laminated body fabricated from magnetic steel sheets laminated in the direction orthogonal to a line normal to the aforementioned magnetic pole surface, with a non-conducting substance between the laminations.
According to the configuration described above, since the first pole body (6) and the second pole body (8) are provided with laminated bodies fabricated from magnetic steel sheets laminated in the direction orthogonal to a line normal to the above-mentioned magnetic pole surfaces, with a non-conducting substance between the laminations, eddy current losses due to flux passing through the yokes can be suppressed, so a magnetic bearing with further reduced losses can be produced.
In addition, the stator cores for a magnetic bearing according to the present invention are contrived in such a manner that the aforementioned first pole body (6) is a laminated body fabricated from magnetic steel sheets laminated in the lateral direction with a non-conducting substance interleaved between each sheet, and the above-mentioned second pole body (8) is a laminated body in which the magnetic steel sheets are laminated in the lateral direction with a non-conducting substance sandwiched between each sheet.
In this configuration, since the first pole body (6) and the second pole body (8) have laminated bodies made of magnetic steel sheets laminated in the lateral direction with a non-conducting substance sandwiched between the sheets, eddy current losses generated when the magnetic flux flows through yokes can be suppressed, so a magnetic bearing with further reduced losses can be offered in practice.
Furthermore, the stator cores for a magnetic bearing that supports a rotor (3) with a supporting surface composed of a magnetic material according to the present invention are formed with N-pole magnetic pole surfaces opposite the aforementioned supporting surface and S-pole magnetic pole surfaces facing the above-mentioned supporting surface, and are made of a magnetic material powder, solidified in resin.
Using the above-mentioned configuration, N-pole magnetic pole surfaces and S-pole magnetic pole surfaces are opposite the supporting surface, therefore, when magnetic flux is passed through the stator cores of a magnetic bearing, N-pole magnetic pole surfaces and S-pole magnetic pole surfaces support the supporting surface of the rotor; because the magnetic material powder, solidified in resin, produces a small amount of eddy current losses, eddy current losses can be suppressed so realizing a magnetic bearing with reduced losses.
Moreover, the stator cores for a magnetic bearing according to the present invention incorporate the rotating shaft of the rotor, eddy current losses are reduced, so the magnetic bearing for a rotor with a small amount of losses can be developed.
Other objects and advantages of the present invention are revealed in the following paragraphs referring to the attached drawings.